Magnetron casing



m4@ P. L. SPENCER f 2,408,235

MAGNETRON CASING Filed Dec. 17, 1941 Patented Sept. 24, 1946 y i, MAcrNE'raoNfcasind c Percy L. Spencer, West Newton, Masts.,

Raytheon Manufacturingv Company, Newton;

Mass.,'a corporation of Delaware i This invention relates to amagnetron casing, and more particularly to such aA casing which is made of a metal, such as copper, and is provided with a special end construction `to increase `the effective magnetic iield within the magnetron,

t `In magnetron tubes of the conductive envelope type, themagnetic el'd is impressed ori the'tubes by magnetic poles placed adjacentbtheopposite ends of thetube. Thus there is an leffective air gap'between the poles extendiigltiie entire length calme-magnetron ,The 'metallic wallsI of the envelope must 'necessarily be of a certain thickness in order to possess the requisite rigidity to withstand the differential atmospheric pressure inside and outside of the tube. This length kof air gap makes it difficult to produce magnetic fields of the desired highintensity in the discharge space within the magnetron.

An object of this invention is to devise a magnetron casing in which the effective air gap length between the magnetic poles is substantially decreased.

Another object is to produce such a structure in which the reduction in air gap is accomplished by the use of highly magnetic end caps provided with means whereby these caps may be readily secured in place as by soldering.

The foregoing and other objects of this invention will be best understood from the following description of an exempliiication thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a vertical cross-section through a magnetron incorporating my invention, taken along line I-I of Fig. 2; and

Fig. 2 is a top view of the magnetron as illustrated in Fig. 1. Y

Y The magnetron illustrated comprises an envelope I which is preferably made of a block of non-magnetic conductive material, such as copper. This block forms the anode of the magnetron, and is provided with hollow end sections which are covered by end caps 2 and 3likewise of conductive material. Between the hollow end sections of the envelope I is the central bridging portion II. The portion 4 is provided with a central bore 5 within which is supported substantially at the center thereof a cathode 6, preferably of the indirectly-heated oxide-coated thermionic type. The cathode 6 is supported by a pair of cathode lead-in conductors 'l and 8 sealed through the ends of glass chambers 9 and I0 on the outer ends of pipes II and I 2 hermetically fastened within the walls of the envelope I adjacent the upper and lowerl hollow end sections.

' entirely of iron,

c comms. (c1. 25p-gral An .additional lead 'I3 may be provided to extend from' a'fs'uitalble'coupling means within the envelope -I', ,whereby high frequency oscillation generated within the device may be conducted to a suitable utilization device. The lead I3 may likewise be sealed through the 'outer end of a glass.l chamber Ilmounted at theL oute'd end of the pipe ,I5 'likewise hermetically sealed within the walls of [the envelope l. The magnetron is designed andintendedto be placed between suitfable1-mag'ne'tic p'o'les I6.Y andy I f'lto create a longitudinal vmagneticl eld passing through the space between the cathode B and the surrounding walls of the bore 5, constituting [the anode structure for said cathode.

If the end caps 2 and 3 were made entirely of copper, it will be seen that the air gap between the poles I6 and I1 would extend the entire length ofthe envelope I. crearte high intensities ofy magnetic elds within the discharge space around the cathode 6, the presence of a relatively long air gap makes it difficult to set up fields of the desired intensity. Thus any way in which the length of this air gap can be decreased will greatly increase the effectiveness of the magnetron device. However, as already indicaited, it is necessary that the wall thickness of the end caps 2 and 3 be a substantil value in order to withstand the atmospheric pressure exerted upon them. One way in which the air gap might be decreased would be to make the end caps entirely of a magnetic material, such as iron. However, if the end caps were made serious difficulties would arise in attempting to hermetically seal the iron'end caps to the copper walls of the envelope I. In accordance with my invention, the end caps, for example the upper cap 2, is made of a thin copper sheet I8 formed into a cup shape fitting relatively snugly within the open upper end of theehvelope I. A plate 20 of a magnetic material, such as iron, is fitted into the upper open end of the cup thus formed. The plate 20 may be fastened within the cup in any suitable way, as by soldering, so as to form a composite wall of the requisifte physical strength. However, it is not necessary to have the connection between the iron plate 20 and the copper sheet I8 in any way hermetic inasmuch as the copper plate I8 in itselfforms an imperforate and impermeable wall against the passage of atmospheric gases into the 1 device. The plate I8 may be sealed-to the wall -of the envelope I along the joint 22 in some suitable way, as by silver solder. This method of sealing two copper members together so as to Since it is desired to construction as described above as many equiva-v lents will suggest themselves to those skilled in the art. For example, instead of having the magnetic plates extend across substantially the entire end of the magnetron, they could be `of'a more limited extent so as to concentrate th'e magnetic eld in the device 'more nearly along the central bore where the greatest concentration of the field is desired. Also the principles of this invention might be applied to various other types of devices utilizing the magnetic iield in which the size of the envelope plays a substantial part in limiting the magnetic field by introducing a substantial airgap.

What is claimed is: Y.

1. A magnetron comprising a hollow envelope of a substantially non-magnetic metal containing cooperating electrode elements, said magnetron being designed and adapted to have a magneticiield set up in the space between said electrode elements,said envelope h'aving an end cap sealed to and closing one end of said hollow envelope, said end cap comprising a sheet of a substantially non-magnetic metal and an insert of magnetic material set into said sheet to decrease the gap space through which said magnetic eld must pass.

2. A magnetron comprising anhollow envelope composed substantially of copper and containing cooperating electrode elements, said magnetron j being designed and adapted to have a magnetic Yiield set up in the space between said electrode elements, said envelope having an end cap sealed to and closing one end of said hollow envelope,

AsaidY end` cap comprising a sheet of copper and an insert of magnetic material set into said sheet to decrease the gap space through which' said magnetic-eldmust pass.

31. A magnetron comprising a hollow envelope composed substantially of copper and containing cooperating electrode elements, said magnetron being designed and adapted to 'have a magnetic eld VSet` up inthe space between said electrode elements, said envelope having an end cap sealed to' andY closing one end of said hollow envelope, said end cap comprising a sheet of copper and an insert of magnetic material set into said sheet to decrease the gap space through which said magnetic eld must pass, said sealing being made between the copper part of said end cap and th ,copper of `said envelope.

' PERCY L. SPENCER. 

